Color-signal detection system



B. D. LOUGHLIN COLOR-SIGNAL DETECTION SYSTEM Original Filed May l, 1950 Dec. 27, 1955 United States Patent O comu-SIGNAL nErEcrIoN sYsrEM Bernard D. Loughlin, Lynbrook, N. Y., assignor to .Hazeltine Research, Inc., Chicago, Ill., a corporation of Illinois Original application May 1, 1950, Serial No. 159,212. Divided and this application July 8, 1952, Serial No. 297,739

11 Claims. (Cl. 178-5.4)

General V"The present invention relates, in general, to colorsignal detection systems for color-television receivers of a three-color television system and, particularly, to such detection systems in television systems which translate brightness information as one signal and chromaticity information as modulation components of a subcarrier wave signal. The present application is a divisional application of applicants copending application Serial No. 159,212, tiled May 1, 1950, and entitled Color-Television System.

In a form of a color-television system, as more fully described in the application previously referred to, color signals individually representative of the primary colors, specifically, green, red, and blue, of a color image being televised are developed at a transmitter. Components of these color signals are applied as modulation signals to a subcarrier wave signal effectively to multiplexmodulate the wave signal by developing in a predetermined phase sequence at diierent phase points thereof modulation components individually representative ofthe primary color signals. Conventionally, the modulated subcarrier wave signal has a predeterminedmean frequency within the vdeo-frequency range and has amplitude and phase charactersitics related to the primary colors of the televised image. In a specific form of such color-television system the subcarrier wave signal is electively modulated at 120 phase intervals by successive ones of the three color signals. In another specific form of such color-television system the subcarrier wave signal may be effectively modulated at 180, and 270 by different'ones of the three color signals. In addition to the modulated subcarrier wave signal, a signal representative of the brightness of the image, in other words a signal including the detail information of the image in terms of shades of black and white, is also developed at the transmitter. The multiplex-modulated subcarrier wave signal, effectively comprising the chromaticity information, and the brightness signal, effectively comprising the brightness and detail information of the televised image, are combined in an interleaved manner to form in a pass band common to both signals a resultant video-frequency signal which is transmitted in a conventional manner. n

A color-television receiver in such color-television `system intercepts the transmitted signal and initially the video-frequency detector derives therefrom the `modulated subcarrier wave signal and the brightness signal, in a conventional manner, as components of a videofrequency signal. The brightness signal has many of the characteristics of a conventional monochrome signal and is conventionally applied directly lto one of the beamintensity control circuits of a picture tube. The modulated subcarrier wave signal is applied toa color-signal detection system to which there is also applied alocally generated signal having a frequency equal to the mean `frequency of the subcarrierwave signal kand having a phase related in phase therewith. A number of color- 'ice nal signals representative of different ones of the threeprimary colors utilized in the color-television system. The derived signals repersentative of the chromaticity of the televised image are then individually combined with the brightness signal to develop in the picture tube a color reproduction of the televised image.

Color-television receivers of the type just described normally include conventional radio-frequency and intermediate-frequency amplifier sections and a conventional detector for deriving video-frequency signals including the brightness and chromaticity information. Such receivers diier from the conventional monochrome receivers in the design of that portion of the receiver following the video-frequency signal detector. In addition to Vother circuits which need not be considered in detail for the purposes of the present invention, the portion of the receiver to which reference has just been made includes the color-signal detection devices, previously mentioned herein, and which in combination with one another comprise a color-signal detection system. The presentv invention is particularly directed to new and improved such detection systems.

As previously mentioned, a number of these colorsignal detection devices are utilized for deriving the chromaticity information from the multiplex-modulated subcarrier wave signal. In three-color television receivers where the chromaticity of an image is represented by signals individually representative of three primary colors, three color-signal detection devices for deriving three signals individually representative of the three primary colors are conventionally employed. These three signals and the signal representative of brightness comprise four components of informationwhich are utilized to provide the complete color information for the three primary colors. Since a composite color composed of three primary colors -is capable of being defined by information relating to the brightness, lhue, and color saturation thereof, it appears more desirable and more economical to develop only three independent components of information to define a composite color in place of the four components derived in previous receivers. Since a color-television receiver of the type previously described herein derives a signal representative of brightness, it appears desirable to utilize in such a receiver a color-signal detection system which will derive two signals which define the chromaticity of the image and which in combination with the brightness signal will d efine the composite colors of a reproduced color image.

VSuch a color-signal detection system will utilize less components and, therefore, be more economical to manufacture than prior such detection systems. Therefore, the present invention is directed to a color-signal detection system which derives only two independent signals representative of the chromaticity of a televised image.

It is, therefore, an object of the present invention to provide a new and improved color-signal detection system for a color-television receiver which avoids the aforeprovide a new and improved color-signal detection sys- -teml for a three-color television receiver in whichv only two color-signal detection devices are employed to derive all of the color information.

granata It is still a further objecty of the present invention to provide a color-signal detection system 'for Va. 'three-color television receiver which is simple, economical, and uti- .lizesa relatively small number of circuit components.

In Laccordance .with the present invention, ,a `.color-signal detection system for a .three-color television .receiver comprises ya rst circuit .for supplying vasignal ,primarily representative of the brightness of a televised colorim- Qage, anda YSecond circuit for Supplyinga wave'signalefect'ively having amplitude-modulation components .at `different ,phase ,points thereof representative of individual ones of signals defining the chromaticity of vthe image. The detection system valso includes .a signal generatorfor developing a 'signal having a frequency which is an .intetgral .multiple of .the .frequency of the aforementioned wave Vsignaland a signal-.detection apparatus including as detectors of the .modulation -components of .the wave signal only two ,signal-.detection devices for deriving ,from the wave signal .different modulation components which ,Substantially vcompletely deline .the chromaticity .of .the image. The .signal-detection .apparatus includes a signal- .translating system coupled tothe second-circuit for applying .the wave signal .to the signal-detection devices .anda signal-,translating ,system coupled .to -the generator for applying :the above-mentioned generated signal to these devices. The signal-translating systems have .dilferent signal-translating characteristics for causing the phase ofthe signals translated therethrough to be so modified that the aforesaid generated .signal is in phase with a .predetermined phase of .the wave signal as applied to .one lof the A-devices and is `substantially in quadrature phase with this predetermined ,phase of ,the wave signal as Yapplied yto the .other f the devices, whereby the different modulation components are individually derived substantially .from quadrature .phase points of the wave signal. Finally, the color-,signal .detection system comprises a signal-'combinmeans -responsive .jointly to the brightness .signal and the derived modulation components .for developing ,at least .three effects for use by a three-color display of a three-.color `television receiver.

Fora better understanding of the present invention, together with .other and further objects thereof, reference is .had :to the following description taken in connection with the accompanying drawing, .and its scope will be pointed vout in the appended claims.

yIn the drawing, the iigure is .a schematic diagram of a three-color television .receiver including a color-.signal detection system ,embodying the invention in one form.

General description of the three-color television receiver Referring to the drawing, there is represented a colortelevision receiver embodying a color-.signal detection system in -accordance with one form of the present invention and comprising portions of Fig. l and Fig. '5 of the aforesaid copending application of which this application is a division. The receiver is of a constant-luminance type as described in the copending application previously referred to. `In other words, it is of a type wherein the monochrome or brightness signal 'determines the brightness of the image, while the chromaticity signals determine "only color and do not aiect brightness. The receiver represented also is of a type ywhich utilizes information representative of the relative proportions of three -primary'colors to be combined toreproduce a color image and is, therefore, designated a three-color television refce'iver. The receiver Yincludes a radio-frequency Vampli- `fier of any desired number of stages having its input circuit connected to an antenna system 11, l11. Coupled in :cascade with the output circuit of the `amplifier 10, in the order named, are an oscillator-modulator 12,'anintermcdiate-frequency amplifier 13 of one or more stages, a .detector and automatic-gain-control (AGC) circuit V14, and a `signal-translating system including 'a color-'signal detection system 15, Ato 'be described in more detail here- 5. inafter, and a color image-reproducing apparatus 16 of 'the 'cathode-raytube type.

As explained more fully in the copending application previously referred to herein, the apparatus 16 comprises cathode-ray tubes 17a, 17h, 17e individually arranged to respond, respectively, to .signals developed in the output circuits of the .unit 15" representative ,of Vthe green, red, and blue colors of the image being televised. In other words, the tubes 17a, 1717, and 17C are arranged to -develop, respectively, green, red,.and blue .images on the respective image screens thereof. The axes of Athe tubes 17a, 1711, and 17C 1are vphysically positioned Vat right angular relationships with respect .to each other, and an optical system 18, which may consist of a Well-known dichroic mirror type arrangement, is so positioned as optically to combine the images on the screens of the cathode-ray tubes 17a, 17b, and 17e into a color reproduction of the televised color image. Conventional beam-deflecting windings are associated with each cathode-ray tube.

Tlhere is valso :coupled to thefdetector 14 a synchronizing-signal separator '19 having output circuits coupled ithrough-a 'line-scanning ygenerator 20 and a field-scanning generator 42.1 `to cach of the vbearn-deilecting windings -of the cathode-ray .tubes 17a, 17b, and 17C. An output circuit-.of the separator 219 isalso connected to a color wavelsignal i'generator 2 in -the system 15".

The :outputcircuitfof :the AGC supply included Vin the unit -14 is yconnected tothe input .circuits of one or more of the tubes of the radio-frequency amplifier lil, the oscillater-'modulator '1.2, andthe Aintermediate-frequency amplifier .1'3 in awell-Lknown manner. A sound-signal reproducing .unit S23 is also connected to the output circuit of the Ain'terrnediate-frequency Vamplifier 13 and may include one .or more stages o'f intermediate-frequency ampliiica- '.tion, a sound-signal detector, one or more stages of audio- -frequency amplification, and a vsound-reproducing device.

'It vwill beunderstood that the various units thus far described with respect to the receiver represented in the drawing, with the exception of the color-signal detecrtion ysystem 15", correspond -to units described in Fig. `l `of lthe aforesaid `copending Aapplication land may have any conventional 'construction and design, the details of such uni-ts being well known in the am, thus rendering a .further description thereof unnecessary.

'General operation of the television receiver Considering briefly the operation of the receiver of Fig. l as a whole, vand assuming for the moment that vthe unit '15 is a means :for developing separate signals representative, respectively, of the green, red, Vand blue colors 'of the image being reproduced, the desired television `signal is intercepted by the antenna 11 and selected and amplified inthe radio-frequency amplifier 10. The latter `signal is :then applied to the oscillator-modulator `12`wherein itis converted into an intermediate-frequency signal `whichis then selectively amplified in the amplier "13 -and supplied to the `detector 14 wherein its modulation components `are derived` The derived composite videofreguency components are applied to the system. 15" wherein signals representative of the green,l red, and blue colors of the televised image are derived from -the applied signal. Individual ones of the derived color signals 'are 'applied .to 'different -ones of -the control electrodes of the cathode-ray tubes 17a, 17b, and 17e in the unit .'16'10 modulate the intensity of the electron beams in these tubes. The synchronizing-signal lcomponents of the received signal are separated from the video-frequency'components in the unit 19 and are utilized to synchronize vthe operation of the line-scanning and ieldscanning generators20 and 21. These vgenerators supply signals of saW-'toothwave form which-are properly -phased withjreference to the transmitted television signal and which `are applied to the deection windings of -the cathode-ray tubes 17a-17e, inclusive, in the unit 16, lthereby to Adeflect vthe lcathode-ray beams in each tube in two directions normal, to each other.' There is thus reproduced on the image screens of the tubes 17a, 1711, and 17C, respectively, green, red, and blue images representative of the respective primary colors of the image being televised at the transmitter. The dichroic mirror arrangement 18 optically combines the green, red, and blue images on the several image screens and presents the complete reproduced color image to the observer.

The automatic-gain-control or AGC signal derived in the unit 14 is effective to control the amplification of one or more of the units 10, 12, and 13 to maintain the signal applied to the detector 14 and to the sound-signal reproducing unit 23 within a relatively narrow range for a Wide range of received signal intensities.

The sound-signal modulated wave signal accompanying the desired television signal is also intercepted by the antenna system 11, 11 and, after amplification in the amplifier 10 and conversion to an intermediate-frequency signal in the unit 12, it is further amplified in the amplifier 13 and applied to the sound-signal reproducing unit 23. In the unit 23 it is amplified and the soundsignal modulation components derived. The latter components are further amplified by the reproducing device in a conventional manner.

Description of color-signal detection system 15" Referring now in particular to the color-signal detection system 15", this system corresponds to the system described with reference to Fig. of the aforesaid copending application and comprises a first circuit for supplying a signal primarily representative of the brightness of a televised color image. Specifically, this first circuit includes a 0-4 megacycle low-pass filter network 64 coupled between the terminals 25, 25 and an input circuit of each of adder circuits 65a, 65b, and 65C. The color-signal detection system 15" also includes a second circuit for supplying a wave signal effectively having amplitude-modulation components at different phase points thereof representative of individual ones of signals defining the chromaticity of the televised image. Specifically, the second circuit comprises a 2-4 megacycle band-pass filter network 27 coupled between the input terminals 25, 25 and an input circuit in each of a pair of synchronous detectors 2811 and 28C for applying to the latter detectors a 3.5 megacycle subcarrier wave signal modulated by color-signal components representative of green, red, and blue of a televised image.

The system 15" also includes a generator for developing a signal having a frequency which is an integral multiple of the frequency of the modulated subcarrier wave signal, specifically, a color wave-signal generator 22". The generator 22 may be a conventional sine-wave generator including automatic-frequency-control circuits for developing a signal having a frequency of substantially 3.5 megacycles if the frequency of the subcarrier wave signal is 3.5 megacycles. Though not considered in detail herein, the frequency of the generator 22" may in some embodiments be a harmonic of the subcarrier wavesignal frequency. An input circuit of the generator 22", as previously mentioned, is connected to an output circuit of the separator 19 for application of a synchronizing signal thereto to control the operation thereof in synchronism with the operation of a corresponding generator in the transmitter.

The system 15" also includes a signal-detection apparatus including as detectors for the modulation components of the subcarrier wave signal only two signaldetection devices, specically the units 28h' and 28e', for deriving from the modulated wave signal different modulation components which substantially completely define the chromaticity of the image. The units 28b' and 28e' are essentially modulators for developing in the output circuits thereof frequency difference signals resulting from the heterodyning of the modulated subcarrier wave signal and the locally developed wave signal. The

output circuit ofthe unit 28h is coupled through a 0-2 megacycle low-pass filter network 29b and an amplilfier A30b to an input circuit of Van adder circuit 65b,

while the output circuit of the detector 28e is similarly coupled through a 0-2 megacycle filter network 29C and an amplifier 30e to an input circuit of an adder circuit 65e. The circuit elements of the amplifiers 3017 and 30e are so proportioned that these amplifiers individually have gains complementary to gains in corresponding signal-translating channels at the transmitter in order to make the total gains of the separate channels for translating the signals representative of the color of an image from the transmitter through the receiver equal for all such channels. These gains are related to the constantluminance correction employed at the receiver in the form of channel gains, as more fully explained hereinafter and in the aforesaid copending application. As described in that copending application, the gain of the channel for translating the signal representative of green can be considered to be unity or one. With relation to such gain the channel at the transmitter, for translating the signal representative of red may have a gain of $5.23, and, also at the transmitter, the channel for translating the signal representative of blue may have approximately a gain of 1/5. As one factor in the system under consideration to assure that all of the primary colors have the same brightness effects at the receiver so that the chromaticity signals control only the color and do not affect the brightness of the reproduced image and to cause the colors in the reproduced image faithfully to represent the colors in the televised image, the gain of the channel translating the signal representative of green is proportioned to be unity, that of the channel translating the signal representative of red is proportioned to be 2.23, and that of the channel translating the signal representative of blue is proportioned to be 5. Thus, if the total gain of each channel is considered to be in one unit in each channel, the amplifier 30b in the channel for translating the signal representative of red may be such a unit and is therefore proportioned to have a gain of 2.23. For a similar reason, the amplifier 30e is proportioned to have a gain of 5.

The signal-detection apparatus also includes a signaltranslating system coupled to the aforesaid second circuit for applying the previously mentioned subcarrier Wave signal to the devices 28b and 28e', specifically, the two signal paths coupling an input circuit of each of the last-mentioned units to different ones of the output circuits of the filter network 27. Additionally, the signal-detection apparatus includes a signal-translating system coupled to the unit 22 for applying the abovementioned generated signal developed in the unit 22 to the units 281; and 28e' for effecting the derivation of the components of the subcarrier Wave signal, specifically, two signal paths individually connecting different ones of separate output circuits ofthe generator 22 to another input circuit of each of the detectors 281; and 28e. At least one of the signal-translating systems for applying signals to the units 28h and 28e has circuit elements so proportioned for modifying the phase of the signals translated therethrough that the generated signal lis in phase with a predetermined phase of the wave signal as applied to one of the devices 28b, 28C', and is substantially in quadrature phase with this predetermined phase of the wave signal as applied to the other of the devices 28b, 28o'.V For example, the signal path coupling an output circuit of the generator 22 to an input circuit of the detector 28b may be considered to include circuit elements so proportioned that substantially no phase delay with respect to an arbitrary predetermined phase thereof occurs in translating a signal from the generator 22 to the input circuit of the detector 28h coupled to the unit 22, while the signal path coupling the generator 22 to an input circuit of the detector 28e includes circuit elements at the latter input circuit that are so proiportioned that tthe signal translated through :the latter ',pathzstdelayedlby .90 phase twith .respect'tothe fabove- .mentioned predetermined ephase. Though, in `such tex- '-ample, tthe delay eis.'corrsideredas occurring with respect ito :the,-,signal:applied from :the generator :22 toithe yde- A:tector 28f,:it .zshnuld fbe :understood that the delay could vequally :well ,occur inone of athe .paths connecting the :output ;circuitofthezltertnetwork'27 to the detectors 28'b';and .28cf. :Inthe rlatter case, the signal appliedto each .of the last-mentioned detectors from the generator Z2" awnuldfhavertheisame.phase with respect to the pre determined phase. ,Additionallyaphase delays may occur 'lhothinrthe :path :fromthe .generator :22 to the detector 28C' tandftheLpathfrom'the ynetwork.27 to thesarne 'deitector to :clause the quadrature rrelationshipofsthe signals -applieditoathecdetcctorlSc to occur. As described more ifullyiingthe aforesaidtcopendingapplication, the detectors .285 :and 128C" aret-conventionalunits arranged to cause the :signalsfapplied 'thereto .ffrom the generator 22 and the :network F27 to heterodyneand develop signals representative t of l any :frequency :difference in the .applied sig- Anels specifically caused l:by the modulation .components of .fthesubcarrier wavesignal.

:'Einally, the system d5 includes a signal-cornbining meansresponsive.jointly to ithe 'brightness signal andithe modulation tcomponents derived in the unit 15 vfor developing vat leastzthree :effects for use by a three-color display of a :threefcolor .televisionreceiverl More. specically, :suchrcombining `means includes the adder circuits l65L1t,tv65b and 65c,ieachfhaving an output circuit coupled throughterminals 26a, ,26]7, and 26e, respectively, to the control electrode .circuits `of the tubes ta, Ib, .and 17C, respectively, in the image-reproducing device 16. Each ofzthetadder circuits 6561-65@ inclusive, has an input ciricuiteoupledrto thefoutput circuit of the lter network64. Additionally, ithe adder circuit 65a has an input circuit 'Coupled through a-phase-.inverter circuit 66a tothe output 'ireuitqof Ithe lterinetwork 2% and has another input circuitcoup'led through a lvoltage divider 67 and a phasefi-nverter circuitidb'to the output circuit of the ilterlnet- -work :295. -As .will ybe A,explained more fully hereinafter, the phase inverters 66a and db are or" a conventional type for'invertingtheiphase ofthe signalsinthe output circuits yof -the-networks V2911 and .230, respectively. The voltage -divider =iti-7 `is proportioned-toapply to the unit65a a pre- -determined portion of the signal developed in the output -circuit of-the network 29C. .'anytconventional design, -for exainple,leach may comprise ,-aplurality of ysimilar tubes having separate input circuits .anda commonV output circuit.

The adder circuits ,may 'have .Explanation of operation-of color-signal detection system In; general, thereceived signalcomponents derived in the detector 14 .and representing the composite video-frequency signals, including brightness and color information, are :applied `to the terminals 25, Z ofthe network 1'52 The signals `primarily representative of brightness andhavingrequencies ofapproximately 0 4 megacycles are translated .through the filter network 64 and applied to the input circuits ofthe vadder circuits 65a, 6517, and V65 c. The subcarrier wavesignal having amplitude-modu lation components at'dierent phase points thereof lrepresentative of individual ones of the signals delning the chromaticity ofthe iin-age and having, for example, a mean frequency of 3.5 megacycles, is translated through the band-,pass vfilter network 27' and applied to input circuits `of .therdctectors ZSb' and Zc. The detectors Zb and 2SC .also lhave V`a localiy generated 3.5 megacycle wave signalrappliedv-thereto from the generator 22, that signal .applied Eto fthe .detector Zib from the unit 22 being in quadrature :with vthe signal appledircrn thc s' mc unit to .the-.detector 28e. .The detectors .Zb .and 2de are effectively modulators, since the modulated lsubcarrier wave signal and the ilocally ,generatedv signal fheterodyne in :each

vred and blue, respectively.

4detector :fto derive the ,low-frequency .modulation compoynents :of 4the iwavetzsignal. The :detector 2817 developssan outputesignal,representative ofzthe modulation components at, rforaexamplelthe 'phasegpoint 'ofzthe subcarrier wave signal while :the detectorZSc develops output signalsrepvresentative of the components, for example, at 'the 90 Aphase 'point offthe subcarrier wave signal.

"to a referencegain-of the lsignal/representative of green, `whereas the amplifier 3de has a gain of '5 with reference to the reference gain. Thus,las explained in the aforesaid copending application, y'these gains yare effective to cause the color signals developed in the output circuits of the adder circuitsbaudfdclfaithfully to represent the red and blue colors,respectively, ofthe televised image. These gains together with the gainiofthe channel includingithe unit a for translating the signal representative of green and, as will be explained more fully hereinafter, the relative proportions of the signal components in the output circuits of the units'29b and '29C which combine to develop the signal representative of green, areeffective to cause the signals representative of Vthe chromaticity of the image to developthe color thereof while not affecting the brightness of the image.

As rwill be more fully understood from a consideration of Vsignalsof speciocomposition-to be considered herein- .aftenportions ofthe signalsdeveloped in the output cir- .cuits ofthe networks 2% and 29C areinverted in phase in of the'system l15 as presented above,it is apparent that three components of information are derived from the composite video-frequency signal by means of the two detection vdevices lb and 28C' and utilized to develop the three signals representative-of the colors green, red, and blue inthe image to be reproduced. Thus, the signal translated through the network l64 is representative of the brightness Vinformation .of the image, while the signals translated through .the networks 29h and 29C, having `been derived from the subcarrier wave lsignal solely by the two detectors 28h', 28C', are collectively representative of the chromaticity-or color information of the image. Specifically, the signal translated-through the network 29b is a colordierence signal R-Y representative of red while the signal `translated through the network 29C is a color difference signal B--Y representative vof blue where the letters .R and B represent, respectively, -red and blue and the letter Y represents the brightness signal. More detail with respectto Vthese .signals will be presented hereinafter. In addition to being representative of the .primaryfcolors red ,and blue, these signals include components lwhich when properly'combined develop a color diierence signal G-Y representative of green :in the reproduced image. The units 66a and bi-andthe voltage divider 67 are'eifective :to.derive the latter components in properproportion ffrom the .vsignalstranslated :through the networks 2911 and A29C for combination in the adder circuit 65a to develop vthe `color difference 'signal -G-Y representative Vof vthe green offthe image. lhusgthe network I1S includesonly favaala substantially completely define the chromaticity of'the image.

It is helpful to consider a specific example to indicate the manner in which information relative to brightness and the three colors green, red, and blue of an image may be derived from the composite video-frequency signal with the utilization of one channel for developing the brightness signal and only two signal-detection devices for developing the signals representative of the green, red, and blue colors of the image. In a constant-luminance type of color-television receiver such as described in the aforesaid copending application, there are developed color signals G, R, B representative, respectively, of the green, red, and blue colors of the image in the output circuits of the adder circuits 65a, 65b,` and 65e, respectively. The signals G, R, B are developed in the adder circuits just mentioned by combining a brightness signal Y in each of these adder circuits with a color difference signal representative of a component of the chromaticity of the image. As defined by Equation l in the aforesaid copending application, the brightness signal Mis:

The reasons for the relative portions of the G, R, B signals which are combined to develop the brightness signal M are fully explained in the copending application and relate to the constant-luminance characteristic of the television system. The brightness signal M defined by Equation l is translated through the network 64 and applied to each of the adder circuits 65a, 65h, and-65e.

In addition to the brightness signal M, there are also applied to the adder circuits 65a, 65b, and 65C signals representative of the chromaticity of the image, specifically, color difference signals g, r, and b. Signals representative of the later signals are defined by Equations 7, 9, and l of the copending application as the signals at the output circuits of the detectors 28a, 2811, and 28e of Fig. l of that application. The latter signals modified by the gains of the channels through which they are translated, become the color difference signals g, r, and b and are defined as follows:

The signals g, r, and b are applied to theunits 65a, 65b, and 65C, respectively. It is apparent that .as the signal g is added to the signal M in the unit 65a the signal G is developed. Similarly, the signals R and B are developed in the units 6517 and 65C, respectively.

Signals r1 and b1 representative of r and b prior to the amplification in the units 30b and 30o are derived directly at quadrature phase points, for example, at the 180 and 270 phase points, respectively, of the subcarrier wave signal by the detectors 28h' and 28o', respectively. These signals are defined by Equations l1 and l2 of the above-mentioned copending application and, for the present purpose, may be defined in a rearranged form of the latter equations, as follows:

As described in the copending application, and as is evident from an examination of Equation 2, the signal g is composed of portions of the G, R, and B signals in the proportions expressed by Equation 2. These proportions as defined in one form by Equation 17 in the copending application may be defined as follows:

where k is the fractional portion of the signal to be combined with the signal r to develop the signal g.

As defined by Equation 17in the copending application:

10 With such Value for k, substituting the values of rrand b1 as defined by Equations 5 and 6, in Equation 7 the signal g as defined by Equation 2 is developed.

To accomplish the operation defined by Equation 7, the phase vinverters 66a and 66b are utilized to develop the signals r1 and -bi, and the voltage divider 67 is adjusted to apply the fractional portion 0.22 of the signal -bi to the adder circuit 65a, the signal -ri being applied to the same adder circuit by the unit 66a.

Though the example just considered is directed to the derivation of the signals -ri and -kbi by means of actual phase-inverter circuits 66a and 66b and the voltage divider 67, as explained in the copending application, at least some of the latter units may be replaced by an asymmetrical arrangement for deriving the signals g, r, and b. Briefly by deriving color difference signals representative of red and blue at the proper phase angles it is possible to cause a color difference signal representative of green to be equal to the inverse of the derived color difference signal representative of red, thereby eliminating the need for more than one phase-inverting circuit.

The embodiment of the invention just described is one wherein information relating to the three primary colors green, red, and blue is derived from the subcarrier wave signal solely by utilizing the two synchronous detectors 28h and 2SC. By utilizing approximately twothirds of the color-signal detection apparatus that would normally be utilized directly to derive signals representative of the three primary colors, all of the information needed to develop signals representative of the three primary colors is obtained. This information is obtained without any loss in the quality of the image reproduced from the derived signals and with evident increased economy in the number of circuits utilized. Though there has been described a specific system for developing signals representative of the three primary colors from two signals derived from the subcarrier wave signal, it is to be understood that signals other than those described herein as being derived from the subcarrier wave signal may be developed and utilized to provide information relative to the three primary colors in accordance with the teaching of the invention.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A color-signal detection system for a three-color television receiver comprising: a first circuit for supplying a signal primarily representative of the brightness of a televised color image; a second circuit for supplying a wave signal effectively having amplitude modulation components at different phase points thereof representative of individual ones of signals defining the chromaticity of said image; a generator for developing a signal having a frequency which is an integral multiple of the frequency of said wave signal; a signal-detection apparatus including as detectors for the modulation components of said wave signal only two signal-detection devices for deriving from said wave signal different modulation components which substantially completely define said chromaticity of said image, including a signal-translating system coupled to said second circuit for applying said wave signal to said devices and a signal-translating system coupled to said generator for applying said generated signal to said devices, said signal-translating systems having different signal-translating characteristics for causing the phase of the signals translated therethrough to be so modified that said generated signal is in phase with a predetermined phaseof said wave signal as applied to one of said devices and is substantially in quadrature phase with said predetermined phase of said wave signal as applied to said other of said "devices, :whereby .said y.different modulation ycomponents fare individually derived substantially from quadrature- `said derived modulation .components vfor developing -at least 4three effects for use by a three-color display of a ithree-'colortelevision receiver.

2. A color-signal detection system for a three-color television receiver comprising: a first-circuit for ysupplying La signal primarily representative of the brightness-of a :televised color image; a second circuit for supplying a 'wave signal efective'ly'having amplitudefmodulation :com- Jponents at different phase points thereof representative roftindividual ones of signals defining the chromaticity fof -said image; agenerator'for developing a signal havinga lfrequency the same as Athe frequency of said wave signal; `ra signal-detection apparatusincluding as detectors for the imodulation components of said wave signal only two sig- `nal-detection devices for derivingfrom .said wave signal -fdifferent modulation components which substantially completely define said chromaticity of saidimage, including -a LAsignal-translating system coupled to said second circuit for vapplying said wave `signal to said devices and a signaltranslating system coupled to said generator for applying "said generated signal to said devices, said signal-trans- "lating systems having different signal-translating characteristics for causing the phase of the signals translated therethrough to be so modified that said generated signal is-in phase with a predetermined phase of said wave signal -as applied to one of saiddevices and is substantially inquadrature phase with said predetermined phase of said -wave signal as applied to said other of said devices, where- 'bysaid diierent modulation components are individually Vderived-substantially from quadrature-phase points ofi-said vvwave signal; and a signal-combining means responsive jointly 'to said brightness signal and said derived modula- -tion components for developing at least three effects l'or use by a three-color display of a three-color television -receiver.

A3. A color-signal detection system for a three-'color television receiver comprising: a iirst circuit for supplying a signal M primarily representative of thebrightness of a -televised color image; a second circuit for supplying a wave signal effectively having amplitude-modulation components at different phase points thereof representative of individual ones of color difference signals g, r, and'b defining the chromaticityof said image in terms-of green, red, and blue, respectively; a-generator for developing a signal having afrequency which-is an integral multiple of the frequency of said wave signal; a signal-detection apparatus including as detectors for the modulation components of said wave signal only two signal-detection devices for deriving from said wave signal only two of said color difference signals g, r, and b, including a signal- 'translating 4system coupled to said'second circuit for applying said wave-signal to'said devices and la-signal-'transl-ating system coupled to said generator for applyingisaid generated signal to said devices, said signal-translating ysystems having different signal-translating characteristics for causing the phase of the signals translated 'therethrough to be so modified that saidv generated signallisin phase with a predetermined phase of said'wave signal as appliedto one of said devices and is substantiallyin 'quadrature phase with said predetermined .phase of said wave signal as applied to said other of said devices,- whereby said two ot said color difference signals g, r, and b are individually derived substantially from quadrature-phase points .of said wave signal; a signal-combining apparatus responsive to at least one of said two of said color difference Vsignalsg, 1', and b for developing the third thereof; Aand a signal-combining-means responsive jointly to said lbrightness:signal and said derivedrnodulation components Vfor Adeveloping at least-three :eects for .use 'by a three- Vcolor displayz of ya ythree-colortelevision receiver.

12 c4. .Asador-signal: detection system for a'three-.color'television receiver comprising: a first circuit for supplying a VVsignal iprimarily lrepresentative Iof .the brightness of a 4televised colorimage; a "second circuit for supplying a wave signal eiectively'having amplitude-modulation corn- 'ponents 4at .diierent phase points thereof representative -of individual ones of signals defining the chromaticity of said image; a `sine-wave signal'generator for developing a signalhaving a-.frequency which is an integral multiple of the frequency'of said wave signal; a signal-detection apparatus including as .detectors for the modulation com- ;ponents of :said zwave signal ,only two signal-detection dev-vicesztor deriving =fromsaid wave signal different modu- Vlation components `whichsnbstantially completely define saidchromaticity .ofrsaid image, including a signal-translating system coupledzto said second circuit for applying said-wavesignal to said devices and a signal-translating .systelncoupled to said generator yfor applying said gen- --eratedzsignal .to .saiddevices, said signal-translating systems having different:signaltranslating .characteristics for causing the -tpha'se of :the .signals translated therethrough to be so modified that -said generated signal is in phase with a predetermined phase of said wave signal as applied -to one-of said devices and is substantially in quadrature 4phase with said predetermined phase of said wave signal as applied `to said other of said devices, whereby said 4different modulation components are individually derived wave signal effectively having amplitude-modulation components at dilerent phase points thereof representative of individualfonesofsignals defining the chromaticity of said image; -a=generator for developing a signal having a frequency which is an integral'multiple of the frequency =of said wave signal; va signal-detection apparatus including as detectors for the modulation components of said wave signal only twosignal-detection devices for deriving from said wave signal difierentmodulation components which substantially completely-dene said chromaticity of said image, including a signal-translating system coupled to said .second circuit 'for applying said wave signal to said devices `and a signal-translating system coupled to said generator -for applying said ,generated signal to said devices, said signal-translating systems having diierent signal-translating characteristics for causing the phase of 'the signals translated therethrough to be so modified that said ygenerated signal is in `phase with a predetermined phase f said wavesignal as applied to one of said devices -and is 'substantially inquadrature phase with said predetermined phase `of said wave signal as applied to said other of said devices, whereby said different modulation components are individually derived substantially -from quadrature-phase points of said wave signal; and a plural- .ity of adder circuits Iindividually responsive jointly to said 'brightness signal'and different ones of said derived modulation components for developing at least three effects :for use by a three-color display of a-three-color television receiver.

6. A color-signal detection system for a three-color 'television `receiver comprising: a first circuit for supplying a signal M primarily representative of the brightness of a televised color image; a second circuit for supplying a wave signal eectively having amplitude-modulation vcomponentsfat-different phase points thereof representaof said wave signal; a first signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said wave signal at one phase point thereof a component representative of said color difference signal Yr; a second signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said Wave signal at another phase point thereof a component representative of said color difference signal b; a signal-developing apparatus responsive jointly to said derived signals representative of said color difference signals r and b for developing a component representative of said color difference signal g; and a signal-combining system responsive jointly to said brightness signal M and said derived and developed components representative of said color difference signals r, b, and g for developing at least three effects for use by a three-color display of a three-color television receiver.

7. A color-signal detection system for a three-color television receiver comprising: a first circuit for supplying a signal M primarily representative of the brightness of a televised color image; a second circuit for supplying a Wave signal effectively having amplitude-modulation components at different phase points thereof representative of individual ones of color difference signals g, r, and b defining solely the chromaticity of said image in terms of green, red, and blue, respectively; a generator for developing a signal having a frequency the same as that of said wave signal; a first signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said Wave signal at one phase point thereof a component representative of said color difference signal r; a second signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal including a circuit for delaying the phase of one of said Wave signal and said developed signal for deriving from said wave signal at a phase point thereof in quadrature with said one phase point a component representative of said color difference signal b; a signal-developing apparatus responsive jointly to said derived signals representative of said color difference signals r and b for developing a component representative of saidl color difference signal g; and a signal-combining system responsive jointly to said brightness signal M and said derived and developed components representative of said color difference signals r, b, and g for developing at least three effects for use by a three-color display of a three-color television receiver.

8. A color-signal detection system for a three-color television receiver comprising: a first circuit for supplying a signal M primarily representative of the brightness of a televised color image; a second circuit for supplying a Wave signal effectively having amplitude-modulation components at different phase points thereof representative of individual ones of color difference signals g, r, and b defining solely the chromaticity of said image in terms of green, red, and blue, respectively; a generator for developing a signal having a frequency the same as that of said wave signal; a first signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said wave signal at one phase point thereof a component representative of said color difference signal r; a second signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said Wave signal at another phase point thereof a component representative of said color difference signal b; a signal-developing apparatus including a phase inverter responsive to one of said derived signals representative of said signals r and b and an adder circuit coupled to said phase inverter for developing a component representative of said signal g; and a signalcombining system responsive jointly to said brightness signal M and said derived and developed components representative of said color difference signals r, b, and g for developing at least three effects for use by a threecolor display of a three-color television receiver.

9. A color-signal detection system for a three-color television receiver comprising: a first circuit for supplying a signal M primarily representative of the brightness of a televised color image; a second circuit for supplying a wave signal effectively having amplitude-modulation components at different phase points thereof representative of individual ones of color difference signals g, r, and b defining solely the chromaticiy of said image in terms of green, red, and blue, respectively; a generator for developing a signal having a frequency the same as that of said wave signal; a first signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said wave signal at one phase point thereof a component representative of said color difference signal r; a second signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from said wave signal at another phase point thereof a component representative of said color difference signal b; a signal-developing apparatus responsive jointly to said derived signals representative of said color difference signals r and b for developing a component representative of said color difference signal g; and a plurality of adder circuits individually responsive jointly to said brightness signal M and different ones of said derived and developed components representative of said color difference signals r, b, and g for developing at least three effects for use by a three-color display of a threecolor television receiver.

l0. A color-signal detection system for a three-color television receiver comprising: a first circuit for supplying a signal primarily representative of the brightness of a televised color image; a second circuit for supplying a wave signal effectively having amplitude modulation components at different phases thereof representative of individual ones of a plurality of color-difference signals defining the chromaticity of said image; a generator for developing a signal having a frequency the same as that of said wave signal; a first signal-detection device coupled to said second circuit and to said generator and responsive to said Wave signal and said developed signal for deriving from one phase of said wave signal a component representative of one of said color-difference signals; a second signal-detection device coupled to said second circuit and to said generator and responsive jointly to said wave signal and said developed signal for deriving from another phase of said Wave signal a component representative of another of said color-difference signals; a signal-developing apparatus responsive jointly to said derived signals representative of said color-difference signals for developing a component representative of a third of said color-difference signals; and a signal-combining system responsive jointly to said brightness signal and said derived and developed components representative of said color-difference signals for developing at least three effects for use by a three-color display of a three-color television receiver.

1l. A color-signal detection system for a three-color television receiver comprising: a first circuit for supplying a signal primarily representative of the brightness of a televised color image; a second circuit for supplying a wave signal effectively having amplitude modulation components at different phases thereof representative of individual ones of a plurality of color-difference signals defining the chromaticity of said image; a generator for developing a signal having a frequency the same as that of said wave signal; a first synchronous detector coupled to said second circuit and to said generator and responsive to said wave signal and said developed signal for derived signals representative of said color-difference signals for developing a component representative of a third of said color-difference signals; `and a signal-combining system responsive jointly to said brightness signal and said derived and developed components representative of 15 said color-difference signals for developing at least three effects for use by a three-color display of a three-color television receiver.

References Cited in the iile of this patent UNITED STATES PATENTS 2,554,693 Bedford May 29, 1951 2,558,489 Kalfaian lune 26, 1951 2,580,903 Evans Jan. 1, 1952 2,635,140 Dome Mar. 14, 1953 2,664,462 Bedford Dec. 29, 1953 

